Process for the preparation of carbon fibers



United States Patent 3,529,934 PROCESS FOR THE PREPARATION OF CARBONFEBERS Akio Shindo, Ikeda-shi, Japan, assignor to Nippon Carbon CompanyLimited, Tokyo, Japan No Drawing. Filed Jan. 4, 1968, Ser. No. 695,560Claims priority, application Japan, Jan. 6, 1967, 42/1,300; Jan. 9,1967, 42/1,700; Feb. 20, 1967, 42/11,044

Int. Cl. C01b 3. /07; D06c 7/04 US. Cl. 23-209.1 12 Claims ABSTRACT OFTHE DISCLOSURE Carbonaceous and carbon fibers of an improved quality areproduced from each of cellulosic, polyvinyl alcoholic and acrylic fibersat a high yield by subjecting it to heat treatment in an acidicatmosphere containing a gaseous hydrogen chloride, which has been foundto be effective for the manufacture of carbon fibers.

This invention relates to carbon fibers, and more particularly, to aprocess for the preparation of carbon fibers by an improved stepincluding a novel chemical treatment.

With a recent development of industrial application of carbon fiber dueto miscellaneous advantages inherent in it, many and varied methods forthe manufacture thereof have been proposed in the past.

The group of starting fibrous materials for which the process of thepresent invention is applied includes the polymeric fibers containingoxygen or nitrogen atoms in their molecules and being thermally stableat 200 C. in an inert atmosphere. The most exemplary polymeric fiberscoming under this group are cellulosic, polyvinyl alcoholic, acrylic,polyimide and polyamide fibers. The details of a process for themanufacture of a carbon fiber from each of cellulosic, polyvinylalcoholic and acrylic fibers as a starting material will be describedhereinafter.

In reference to the method for making carbon fiber from the abovefibrous material, it is known that there is a two-step process whichcomprises subjecting the fiber to a heat treatment in an atmospherecontaining oxygen, such as, air at a relatively low temperature between100 and 500 C. in a first step, and subsequently, to a next heattreatment in an inert atmosphere, such as, nitrogen at a relatively hightemperature above 500 C. in a second step. In order to increase theyield of carbon fiber as well as improve its quality, it is also knownthat in the first step of the above process the fibrous material istreated with a compound selected from the group of zinc chloride, ironchloride, aluminum chloride, magnesium chloride and calcium chlorideprior to the heat treatment.

I, inventor of the present invention have discovered based on myexperimental researches on the preparation of carbon fibers that thecarbon fiber produced by a novel process of this invention whichcomprises subjecting the fibrous material to a heat treatment in anatmospehere containing acid vapor, in particular, nonoxidizing acid, inthe low temperature step of the known method.

Furthermore, I, inventor, have also discovered that when the fibrousmaterial is subjected to a predetermined tension while treated in theatmosphere containing acid vapor, such as, hydrochloric acid, theresulting fibrous carbon product has a higher tensile strength as wellas a higher modulus than that of the one of prior art.

The known process of making carbon fiber from the fibrous materialconsists of the two steps described above.

In accordance with a preferred embodiment of the invention, however, ithas been found that the manufacture of carbon fiber is feasible bysubjecting a fibrous material to a single treatment step in an acidicatmosphere, in particular containing hydrochloric acid, at a temperaturein the range of C. to 1500 C., and further, at a high yield togetherwith a good quality.

As described hereinbefore, a fibrous material adapted for the process ofthis invention including the novel chemical treatment includes acellulosic fiber such as, for example, cotton and other naturalcellulose, rayon, regenerated cellulose, such as, cellulose nitrate,polyviriyle alcoholic fiber, polymeric fiber containing vinyl alcohol inpolymer form, and acrylic fiber, containing acrylonitrile in polymerform.

This invention relates to the method of making a carbonaceous or carbonfiber from the above fibrous material and it is to be understood that inthe invention carbon fiber includes a blackened fiber by heat treatmentand a graphitized fiber as well. It is also understood that fiberincludes short and long ones, yarn, string, felt, woven cloth and othervarious forms.

It is already known that a fibrous carbon product is obtained bysubjecting a fiber material to heat treatment only in an inertatmosphere at a predetermined temperature for a predetermined. period oftime. However, it is also known in this case that the yield ofcarbonization of fiber is considerably low while the strength of aresulting fibrous carbon product is exceedingly low. For example, it hasbeen found that when a cotton material, containing cellulose, issubjected to heat treatment in an inert atmosphere at a temperature of300-400 C., the loss of weight of fiber occurs in the order of about 75%by weight, and furthermore, the yield of carbonization of fiber whenheated up to 600 C. barely amounts to about 12%. One of known processesfor the increase of carbonization yield of fibrous material consists intreating a cellulosic fibrous material with metallic chloride, such as,aluminum chloride described hereinabove, and subsequently firing it inan inert atmosphere.

In accordance with a preferred embodiment of the invention, one of theabove fibrous materials is subjected to heat treatment in an atmospeherecontaining gaseous hydrochloric acid at a temperature of 3000 C.,whereby the fiber material is carbonized in a more efiicient manner thanin the conventional process for making carbon fiber. It is to be notedthat the gaseous or vaporous hydrochloric acid has been found to be aneffective agent for eliminating oxygen and nitrogen together withhydrogen, in the form of Water and ammonium, from the fiber in thecarbonization process. It is a widely accepted conception thathydrochloric acid and the like have no such function. On the contrary,however, it as been found that the gaseous hydrochloric acid and thelike exhibit a good catalytic function for carbonization in themanufacture of carbon fiber from the fibrous materials.

Accordingly, it is an essential object of the invention to provide aprocess for the manufacture of a good quality carbon fiber at a highyield from a fibrous material by the application of the acidicatmosphere containing hydrochloric acid and the like to the fibrousmaterial in a heat treatment step.

It is a further object of the invention to provide a process of making acarbon fiber having various degrees in properties.

It is another object of the invention to provide a process of making agood carbon fiber at a high yield by a novel method including a novelchemical treatment step.

It is an additional object to provide a process of making a carbon fiberhaving high tensile strength and especially high modulus by applying apredetermined tension to the fibrous material while being heat treatedat a relatively low temperature in an acidic atmosphere containingnon-oxidizing acid vapor.

Other objects and advantages of the invention will be apparent from thedescription of many preferred embodiments.

The following description in accordance with the present invention willbe divided into three sections: (1) cellulosic fiber, (2.) polyvinylalcoholic fiber, and (3) acrylic fiber.

(1) CELLULOSIC FIBER The cellulosic fiber adapted for the process ofthis invention includes a vegetable fiber of natural origin, such as,cotton, hemp, flax, ramie, and Manila hemp, and an artificial fiber,such as, rayon, regenerated cellulose, cellulose nitrate, cupraammoniumrayon, cellulose acetate, saponified cellulose, and a cellulose whichcontains lignin, etc.

Vlflaen cellulosic fibers such as, for example, cotton and rayon areheated in an acidic atmosphere, they begin to decompose, mainly owing tothe progress of dehydration reaction, at a temperature near 100 C. Thecarbonization reaction of them proceeds remarkably in the temperaturerange between 150 and 250 C., and fairly rapidly in the temperaturerange between 250 and 600 C. At the temperature of 600 C. the degree ofcarbonization of them was 90%.

In carrying out the carbonization treatment procedure of the presentinvention for cellulosic fibers, they are heated in an acidic atmosphereat a temperature between 100 and 250 C. and they also can be heated at atemperature between 250 and 600 C. in the acidic atmos phere. The fibersheated in the acidic atmosphere at a temperature between 100 C. and 600C. can be heated at a higher temperature than those temperatures in aninert atmosphere to reach to a higher degree of carbonization. However,to obtain satisfactory results of the carbon fibers, the heat treatmentof cellulosic fibers in the acidic atmosphere is preferable at thetemperature of 250 C. To obtain much more satisfactory results of thecarbon fibers, it is recommended that the heat treatment in the acidicatmosphere should be carried out at a temperature between 150 and 250 C.Furthermore, raising the temperature of the fiber continuously from atemperature near 150 C. to a temperature near 600 C. in the acidicatmosphere is much more preferable to obtain the carbon fibers havinggood qualities. A period of time for which the fibers are heated at atemperature in the range from 150 to 250 C. in the acidic atmosphere ispreferred to be between 30 minutes and hours. If it is sufficient toblacken the collulosic fibers in the acidic atmosphere, a period of timeshorter than 30 minutes also may be employed.

To obtain the carbon fibers having various degrees of properties, thefibers heated at a temperature below 600 C. can be heated in an inertatmosphere at a higher temperature below 3000 C. or the temperature atwhich carbon fiber sublimes substantially. At a temperature below 1500C. the fibers also are preferred to be heated in the acidic atmospherebecause of the eificacy of acid vapor for eliminating impurities in thefibers.

(2) POLYVINYL ALCOHOLIC FIBER The process of this invention as appliedto cellulosic fiber can be also applied to polyvinyl alcoholic fiber,which includes a high polymeric fibrous material containing vinylalcohol in polymer form. The polyvinyl alcohol modified with a partialformalization, a partial acetalization, a partial ketalization, apartial amino-aceta'lization, or a partial esterification can be alsoused. The fiber material containing vinyl alcohol high polymer or acopolymer therewith, or a mixed high polymer can be employed. As a mixedhigh polymer, it includes cellulose or lignin. A vinyl alcoholic polymerwith cross-linking can be used as a starting material. It includespolyvinyl alcoholic fiber material cross-linked with an unsaturatedaldehyde. Each of the polyvinyl alcoholic fibrous material is desirableto contain at least 70% of vinyl alcohol by weight of monomer in polymerform. If below 70%, it can be used, too. A fiber material adapted for astarting material is preferred to be drawn to at least twice theiroriginal as-spun length. It is preferable to use the fiber prepared by adry spinning as the starting fiber.

When polyvinyl alcoholic fibers are heated in an acidic atmosphere, forexample, hydrochloric acid vapor, the dehydration reaction begins toproceeds at a temperature near C., and proceeds rapidly in the rangebetween to 250 C., and slowly in the range between 250 to 450 C. In theheat treatment in an inert atmosphere polyvinyl alcoholic fiber melts ata temperature near 230 C., but it increases remarkably its thermalstability by being heated in an acidic atmosphere at a temperaturebetween 120 C. and 230 C. The polyvinyl alcoholic fibers with thetreatment of dehydration become must more stable thermally by beingoxidized with an oxidizing atmosphere such as, for example, air andchlorine gas.

In order to dehydrate polyvinyl alcoholic fibers, it is possible toemploy aluminium chloride vapor at a temperature above its sublimationpoint, near 180 C. However, acid vapors such as hydrochloric acid ispreferable because of a high etficacy in dehydration and convenience inhandling.

In carrying out the dehydration treatment procedure of the presentinvention for polyvinyl alcoholic fibers, it is recommended that theheat treatment of the fibers should be made to start at a temperaturebetween 150 C. and 200 C.

The fiber heated in an acidic atmosphere at a temperature between 150 C.and 200 C. also is desirable to be heated in an acidic atmosphere at atemperature between 250 C. and 450 C., to obtain the good results of thecarbon fiber after the peroxidation treatment and then the carbonizationtreatment.

The dehydrated polyvinyl alcoholic fibers obtained in accordance withthe dehydration treatment procedure of the present invention are fairlystable thermally, but its thermal stability is not high enough to besatisfied. To reach sufiiciently high thermal stability of thedehydrated fibers, in accordance with the preoxidation treatment of thepresent invention, the fibers are heated in an oxidizing atmospherecontaining air, halogen and the like.

The temperature at which the dehydrated polyvinyl alcoholic fibers arepreoxidized in an oxidizing atmosphere containing chlorine gas isbetween 200 C. and 700 C. With air the fibers are heated at atemperature between C. and 500 C. However, in the preoxidation treatmentwith air it is preferable to heat the dehydrated fibers at a temperaturebetween 200 C. and 350 C. Furthermore, it is recommended to startheating in air at a temperature between 170 C. and 200 C. to accomplishthe preoxidation treatment. In the heat treatment in halogen gases it ispreferable to start heating at a temperature between 200 C. and 400 C.To accomplish the preoxidation treatment, it is preferable to heat thefibers for a period of time between 30 minutes to 20 hours. However, aperiod of time shorter or longer than those also may be employed on thedehydrated fibers. The fibers preoxidized with an atmosphere containingchlorine or bromine are not always necessary to be heated in an acidicatmosphere. However, the fibers preoxidized with an atmospherecontaining oxygen are preferable to be heated in an acidic atmosphere ata temperature below 600 C. or 1500 C. However, the carbon fibers havinggood qualities desired for industrial needs can be obtained by heatingthe dehydrated and then preoxidized polyvinyl alcoholic fibers in aninert atmosphere.

(3) ACRYLIC FIBER The process of this invention as applied to cellulosicand polyvinyl alcoholic fibers can be also applied to acrylic fiber,which includes a fibrous material containing acrylonitrile in polymerform, and besides, a fiber consisting of graft polymer, other copolymersor mixed polymers. Each of the acrylic fibrous materials is desirable tocontain at least 70% of acrylonitrile by weight of monomer in polymerform. If below 70%, it can be used, too. A fiber material adapted for astarting material is preferred to be drawn to at least twice theiroriginal as spun length.

In the carbonization treatment procedure of acrylic fibers, in thepresent invention, the fibers are heated in an acidic atmosphere at atemperature between 150 C. and 1500 C. However, when acrylic fibers areheated in an acidic atmosphere, the carbonization reaction proceedsremarkedly at a temperature between 200 C. and 450 C., and at a lowerrate at a higher temperature than 450 C. However, the rate at which thecarbonization reaction proceeds at a temperature between 450 C. and 800C. is faster than that between 800 C. and 1500 C. Accordingly, it isrecommended that to reach good qualities of the heat treated fibers thecarbonization treatment procedure of acrylic fibers is made to comprisea process of heating them in an acidic atmosphere at a temperaturebetween 200 C. and 450 C. In accordance with the heat treatmentprocedure of the present invention, the fibers heated at a temperaturebetween 200 C. and 450 C. can be heated in an inert atmosphere to obtainthe carbon fibers having properties desired for industrial needs.However, it is preferable to start heating in an acidic atmosphere at atemperature between 250 C. and 350 C., and to further heat in an acidicatmosphere at a temperature above 450 C., to obtain the carbon fibershaving good qualities.

A period of time for which the fibers are heated at a temperature below450 C. in an acidic atmosphere is to be between 20 minutes and 20 hours.However, a period of time shorter or longer than those also may beemployed in the acidic atmosphere treatment.

From the preoxidized acrylic fibers, also the carbon fibers beingsuperior in properties to that obtained by heating in an inertatmosphere can be produced with a higher yield than that by the knownmethod by heating them, in accordance with the carbonization treatmentprocedure of the present invention, in an acidic atmosphere.

The preoxidation treatment is accomplished by heating the acrylic fibersin air at a temperature between 180 C. and 350 C. for a period of timefrom 30 minutes to 20 hours, or by heating the acrylic fibers in anatmosphere containing halogen gas, chlorine or bromine, at a temperaturebetween 150 C. and 350 C. for a period of time between minutes and 5hours.

The rate of carbonization reaction of the preoxidized acrylic fibers ismost rapid in the range between 250 C. and 450 C., and next in order ofthe rate comes the range between 45 0 C. and 800 C. Accordingly, thecarbonization treatment procedure of the preoxidized acrylic fibers inthe present invention is similar to that of the acrylic fibers withoutpreoxidation treatment.

In the present invention, the fibers such as, for example, threads andfabrics of acrylic fiber and polyvinyl alcoholic fiber upon which silicafine powder solids are discontinuously deposited in accordance with theknown method may also be used as one of the starting materials with orwithout the preoxidation trreatment. On these powder solids coatedfibers the heat treatment procedure in an acidic atmosphere describedhereinbefore can be employed. The powder solids deposited on the fiberis preferable to be removed from the fibers after the heat treatmentbelow 45 0 C.

In the course of reaching this invention, it has been found thatimposing stress on the fibers during the heat treatments at atemperature below 450 C. and at a temperature between 2500 C. and 3000C. or above is effective for the increase of tensile strength andmodulus of carbon fibers to be produced.

On each fiber of cellulosic, polyvinyl alcoholic and acrylic fibers,when it is heated, the linear shrinkage occurs substantially below 800C. as one of the results of the progress of decomposition orcarbonization of the fibers. To reach a higher tensile strength of thecarbon fibers, in the carbonization treatment procedure of the presentinvention, a temperature between 150 C. and 450 C. is preferable as thetemperature at which a stress is imposed on the fibers so as to make thelinear shrinkage lower. However, in the treatment at a temperature below450 C., when the stress imposed on the fibers is excessively high orlow, the stress has no efficacy in increasing the tensile strength ofthe carbon fiber products. When the stress is excessively high, thefibers are broken or become lower in its tensile strength.

The rate to which the fibers shrink lengthwise during the heat treatmentdepends on various factors such as the kinds of polymeric material ofwhich the fibers are formed, the thickness of filament of the fibers,the kinds of atmospheric gases and the ways of raising temperature ofthe fibers. Therefore, it is difiicult to give detailed explanation ofthe relation between the rate of the linear shrinkage and these variousconditions. However, the linear shrinkage during the heat treatmentbelow 450 C. of the cellulosic, poly-vinyl alcoholic and acrylic fiberswithout imposed stress were between 14 and 30%, 25 and 55%, and 15 and40%, respectively.

It was found that the 1000 C. carbon fibers having higher tensilestrength by 10-30%, 10-50% and 10-50% than that of the 1000 C. fiberswithout the treatment of imposing stress can be produced from thecellulosic, polyvinyl alcoholic and acrylic fibers, respectively, byimposing stress on them during the heat treatment at a temperature ofbelow 450 C. so as to become the linear shrinkage of 624%, 19-53% and3-24%, respectively. These values of the linear shrinkage correspondedto 40-80%, -97%, and 20-60% of the linear shrinkage during the heattreatment to 450 C. without imposing stress.

Thus, it has been found that when the fibers are imposed a stress at atemperature between 150 C. and 450 C. in such a manner that the linearshrinkage, at a temperature of heat treatment of 450 C., of the fiberswith the treatment of imposing stress become 40-80%, 75-97%, and 20-60%of those of the cellulosic, polyvinyl alcoholic and acrylic fiberswithout the treatment of imposing stress, respectively, the carbonfibers having higher tensile strength can be obtained after thecarbonization treatment of them. However, it is preferable that theratios of the shrinkage of the fibers with the treatment of imposingstress against that of the fibers without the treatment of imposingstress are 50-60%, and 25-40% for the cellulosic, polyvinyl alcoholicand acrylic fibers, respectively.

It has been found that in the heat treatment at a temperature above 2500 C. of the carbon fibers with the heat treatment in an acidicatmosphere, the carbon fibers having particularly high modulus can beproduced by stretching them with imposing stress. This stretchingtreatment is efficacy in increasing the modulus of the carbon fibersproduced from, in particular, the polyvinyl alcoholic and acrylicfibers, because they (carbon fibers) have such a structure that carboncrystallites are oriented remarkedly. However, it is preferable that thetemperature at which the fibers are stretched .is above 2700 C. The rateof stretching the carbon fiber can exceed a value of 40% by length andmay be lower than 5%. It is not desirable to stretch the fibers at aexceedingly high speed, because stretching by such a high speed causesthe breakdown of the fibers during the heat treatment. The speed ofstretching the carbon fiber depends on the kinds of the origins ofcarbon fibers, thickness of them and the heat treatment temperature.However, at 2700 C. it can be slower 12% per minutes and at 3000 C. canbe slower than 5-10% per minute. It is to increase the properties of thestretched carbon fibers that the stretching speed is slower than thevalues mentioned above.

The acid vapor for use in the present invention contains hydrochloricacid, bromic acid, formic acid, acetic acid or other acid, nitrous oxidegas, sulfur dioxide gas or other acid anhydride. As the acidicatmosphere for use in the present invention, an inert gas containing oneof these compounds. In practice, however, hydrochloric acid vapor ismost preferred. The term hydrochloric acid vapor here is usedsynonymously with hydrogen chloride gas.

The concentration of acid vapor in the acidic atmosphere for use in thepresent invention is desirable to be above 10% by volume, but below 10%by volume can be used. The pressure of the acidic atmosphere can beselected to be a high pressure above the atmospheric one or reduced.

In reference to the inert atmosphere, nitrogen or argon is usually used,but in practice nitrogen is preferable to use.

At a relativel low temperature at which the carbonization proceedssubstantially, a large amount of decomposing gases is evaporated fromthe fibrous material. These gases tend to deposit on the fibers to becarbonized as soot. To avoid this disadvantage it is preferable to flowalways at a sulficiently high rate a fresh acidic atmosphere or inertone to remove decomposing gaseous products from the fibers.

In the heat treatment of the present invention, it is possible to heatthe fiber at a constant rate of raising ternperature, at a step-by-steptemperature rise, or at a variable rate of raising temperature in acertain temperature range. However, it is preferable that at atemperature below 5 C. the fibers are heated at a rate of raisingtemperature below 00 C./ hr.

The heat treatment of the present invention can be carried out by usingany convenient type tunnel furnace or batch type furnace.

The following Examples 1-11 relate to cellulosic fibers, 12-21 topolyvinyl alcoholic fibers, and 22-35 to acrylic fibers. All thepercentages of yield will be seen in the examples are expressed byweight, and all the percentages of concentration of atmosphere used inthe examples by volume. The composition percentages of the copolymersfrom which the starting fiber material has been formed is expressed byweight of monomer.

Example 1 A loose batt of cotton having a random fiber orientation washeated in an atmosphere of hydrochloric acid vapor from 100 C. to 500 C.Rates of raising temperature in the ranges from 100 C. to 200 C., from200 C. to 300 C., and from 300 C. to 500 C. were 100 C./hr., 500 C./ hr.and 200 C./hr., respectively. A loose batt of highly flexiblecarbonaceous fiber was obtained, with a yield of 41% by weight, whichcorresponded to 270% of the yield of crabonaceous material obtained byheating another batt of the same cotton fiber that used above under thesame condition of raising temperature that employed above only in anatmosphere of nitrogen.

Example 2 A bundle-like mass of viscose rayon filamentary fiber (6denier per filament) was heated from 100 C. to 700 C. in a flow ofacidic atmosphere containing 60% of hydro chloric acid and 40% ofnitrogen by volume. Rates of raising temperature in the ranges from 100C. to 500 C. and from 500 C. to 700 C. were 60 C./hr. and 120 C., hr.,respectively. At 700 C. the fiber was held for one hour. A bundle-likemass of carbon fiber was obtained, with a yield of 37% by weight, whichcorresponded to 320% of the yield of carbon fibers obtained by heatinganother portion of the same fiber that used above solely in nitrogenthough under the same condition of raising temperature that employedabove.

Example 3 A loose bundle-like mass of viscose rayon filamentary fiber (4denier per filament) was heated from 120 C. to 240 C. at a rate of 180C./hr. in a flow of hydrochloric acid vapor, and then in a stream ofnitrogen from 240 C. to 530 C. at a rate of 260 C./hr. and at 530 C. for20 minutes. The product was highly flexible, its yield being 38% byweight, which corresponded to 290% of the yield of the fiber obtained byheating another portion of the same rayon fiber that used above solelyin a nitrogen stream under the same condition of raising temperaturethat employed above.

Example 4 A batt of cotton was heated from 130 C. to 420 C. at a rate of240 C./hr. in a flow of atmosphere containing 30% of hydrochloric acidand 70% of nitrogen, and then in a flow of nitrogen from 420 C. to 1000C. at rates of 350 C/hr. and 450 C./hr. in the ranges from 420 C. to 600C. and from 600 C. to 1000 C., respectively. The fibrous mass was heldat 1000 C. for 20 minutes. The yield was 33% by weight, whichcorresponded to 300% of the yield of the product obtained by heatinganother batt of the same cotton that used above under the same conditionthat employed above solely in a nitrogen gas stream.

Example 5 A bundle-like mass of yarns of rayon filamentary fiber (4denier per filament) was heated from C. to 340 C. at a rate of C./hr. ina flow of hydrochloric acid vapor, and then was heated in a nitrogen gasflow from 340 C. to 900 C. at a rate of 240 C./hr. and at 900 C. for 20minutes. The carbon fiber obtained exhibited an average tensile strengthof 6.8 10 kg./cm. Another bundle-like mass of the same starting fiberthat employed above was heated under the same conditions that describedabove except being held under tension during the heat treatment from 240C to 340 C. The linear shrinkage of this 340 C. fiber was 76% of theshrinkage of the 340 C. fiber ob tained without being held undertension. The 900 C. carbon fiber, with the treatment of imposing stress,exhibited a tensile strength of 8.7 10 kg./cm. and a modulus of 2.9 X10kg./crn.

Example 6 A continuous yarn of rayon filamentary fiber was heated fromC. to 500 C. in a flow of acidic atmosphere containing 70% ofhydrochloric acid and 30% of nitrogen by volume by being moved through aheating zone from 130 C. to 250 C. in 30 minutes and through a zone from250 C. to 500 C. in 25 minutes. The 500 C. fiber was further heated in aflow of atmosphere having the same composition that in the case of heattreatment below 500 C. by being moved through a zone from 500 C. to 800C. in 20 minutes and through a zone at 800 C. in 5 minutes The productexhibited a tensile strength of 5.4 10 kg./cm. and a yield of 36%, whichcorresponded to 300% of the yield in the case of heat treatment in anatmosphere containing only nitrogen. The heat treatment was carried outin a tunnel furnace.

Example 7 A continuous yarn of filamentary fiber of rayon was heated inan acidic atmosphere, containing 80% of hydrochloric acid and 20% ofnitrogen, from 120 C. to 600 C. at a rate of 60 C./hr., and from 600 C.to 1200 C. at a rate of 200 C./hr. This 1200 C. yarn was heated from1200 C. to 2700 C. at a rate of 600 C./hr., and at 2700 C. for 30minutes. During the heat treatment at 2700 C. the yarn was stretched 18%by length by being held under tension. The unstretched 2700 C. fiber ex-9 hibited a modulus of 3.1 X 10 but the stretched 2700 C. fiber amodulus of 140% of this value.

Example 8 A portion of continuous carbon yarn obtained in Example 6 washeated in nitrogen gas by being moved through a zone from 800 C. to 2500C. and through a zone at this latter temperature in 36 minutes. Duringthe heat treatment at 2560 C. the yarn was imposed stress and stretchedby 4% by length. The carbon fiber stretched exhibited a modulus higherby 40% than that of the un stretched 2560 C. fiber which was obtained byheating another portion of the 800 C. yarn in Example 6 under the samecondition that in the case of the stretched fiber except imposingstress.

Example 9 A continuous yarn of rayon filamentary fiber was continuouslyheated in a flow of acidic atmopshere containing 40% of hydrochloricacid and 60% of nitrogen by being moved through a zone from 120 C. to440 C. in 40 minutes. Furthermore, the 440 C. yarn was continuouslyheated in a flow of acidic atmosphere of the same condition that in thecase below 440 C. by being moved through a zone from 440 C. to 700 C. in20 minutes, through a zone from 700 C. to 1100 C. in 20 minutes, andthrough a zone at 1100 C. in 10 minutes. During the heat treatment from120 C. to 440 C. the fiber yarn was imposed stress. The linear shrinkageof the yarn during heat treatment from 120 C. to 440 C. was 53% of theshrinkage of the 440 C. fiber obtained without imposing stress. The 1100C. carbon fiber without the treatment of imposing stress exhibited atensile strength of 7.1 10 kg./cm. and a modulus of 3.2.)(10 kg./ cm.The 1100 C. carbon fiber with the treatment of imposing stress exhibiteda tensile strength of 8.4 kg./cm. and a modulus of 5.4 10 kg./cm.

Example 10 The carbon yarn produced in Example 5 was heated in anatmosphere of nitrogen by being moved through a zone from 1500 C to 300C. and a zone at 3000 C. During the heat treatment for 8 minutes at 3000C. the yarn was imposed stress and stretched by 31%. The unstretched3000 C. carbon fiber yarn exhibited a modulus of 3.6 10 kg./cm. Thestretched 3000 C. fiber yarn exhibited a modulus higher by 170% thanthat of the unstretched 3000 C. fiber yarn.

Example 11 A portion of the carbon fiber obtained in Example 9 washeated in a flow of argon gas from 1100 C. to 2800 C. at a rate of 750C./hr. and was held at this latter temperature for 30 minutes. Duringthe heat treatment at 2800 C. the fiber was imposed stress and stretchedby The 2800 C. fiber obtained by heating another portion of the samestarting carbon fiber that used above under the same condition thatemployed above except without imposed stress exhibited a modulus of3.2)(10 kg./cm. The stretched 2800 C. fiber exhibited a modulus higherby 82% than that of the unstretched 2800 C. fiber.

Example 12 A bundle-like mass of polyvinyl alcoholic filamentarymaterial containing 85% of vinyl alcohol and 15% of vinyl acetate byweight of monomer in polymer form (6 denier per filament) was heated ina flow of hydrochloric acid gas by raising the temperature from 100 C.to 250 C. at a rate of 120 C./hr. and by being held at the lattertemperature for 30 minutes. The fiber was cooled in a stream of nitrogengas. The product was of blackish-brown color and semiconductiveelectrically, and exhibited a tensile strength and a flexibility desiredfor industrial needs. The yield was 66% by weight.

Example '13 A bundle-like mass of filamentary fiber of polyvinylalcoholic material having a degree of saponification of (4 denier perfilament), prepared from polyvinyl acetate, was heated in a flow ofacidic atmosphere containing 40% of hydrochloric acid and 60% ofnitrogen from 130 C. to 250 C. at a rate of 60 C./hr. and from 250 C. to350 C. at a rate of 200 C./hr. The blackish-brown colored fiber obtainedexhibited a strength and flexibility desired for industrial needs. Theyield was 61% by Weight.

Example 14 A bundle-like mass of polyvinyl alcoholic filamentary fiberhaving a degree of saponification of 99% (7 denier per filament) washeated in an acidic atmosphere containing 20% of hydrochloric acid vaporand 80% of nitrogen gas by volume from 100 C. to 200 C. at a rate of C.and from 200 C. to 340 C. at rate of 240 C./hr. The fiber having astrength and flexibility desired for industrial needs was obtained. Thedegree to which the dehydration reaction of the fiber had been in thefiber during the heat treatment Was 96%.

Example 15 The dehydrated polyvinyl alcoholic fiber obtained in Example14 was preoxidized by heating in air successively at a temperature ofC., 180 C., C. and 200 C. for one hour at every temperature. Theblackish-brown colored fiber having an electric semiconductivity wasobtained. During this heat treatment the substantial weight loss did notoccur. The product was thermally stable and exhibited a strength andflexibility desired for industrial needs.

Example 16 The fiber obtained in Example 13 was heated to 250 C. in aflow of nitrogen gas, and then was heated in a flow of chlorine from 250C. to 500 C. at a rate of 60 C./hr. and from 500 C. to 600 C. at a rateof 120 C./ hr. The 600 C. fiber was further heater in a stream ofnitrogen from 600 C. to 1050 C. at a rate of 250 C./hr. and was held atthis latter temperature for 30 minutes. The product exhibited a tensilestrength of 8.9 10 kg./ cm. and a modulus of 7.8 10 kg./cm.

Example 17 The same starting fiber as used in Example 14 and the fiberobtained in Example 15 Where heated in a nitrogen gas flow from 200 C.to 700 C. at a rate of 120 C./hr., from 700 C. to 900 C. at a rate of200 C./hr., and at 900 C. for 30 minutes. The product with the treatmentof dehydration, in an acidic atmosphere, exhibited a tensile strength of9.8 10 kg./cm. and a modulus of 8.2)(10 kg./cm. The yield was 43%. Theproduct without the heat treatment in acidic atmosphere exhibited atensile strength of 3.6 10 kg./cm. and a modulus of 3.2)(10 kg./cm. itsyield being 31%. Other portions of the same dehydrated and preoxidized200 C. fiber that obtained in Example 15 also are heated in a nitrogengas flow from 200 C. to 430 C., with or without imposed stress, underthe same condition of raising temperature that employed above. Thelinear shrinkage of the 430 C. fiber with the treatment of imposingstress was 74% of the shrinkage of the 430 C. fiber without thetreatment of imposing stress. These 430 C. fibers were heated in anitrogen gas flow to 900 C. under the same condition that employedabove. The 900 C. fiber With the treatment of imposing stress exhibiteda tensile strength of 14.8)(10 kg./cm. and a modulus of 11.8 10 kg./cm.

Example 18 A continuous yarn of polyvinyl alcoholic filamentary fiber (6denier per filament) was heated in a flow of atmosphere containing 80%of hydrochloric acid and 20% of nitrogen, in a tunnel furnace, by beingmoved continuously through a heating zone from 120 C. to 230 C.

in 40 minutes and through a zone from 230 C. to 340 C. in 15 minutes.This fiber was heated in air by being moved through a zone from 170 C.to 250 C. in 30 minutes. The fiber product was thermally stable andflexible, and exhibited a tensile strength desired for industrial needs.Another portion of the same starting fiber that used above also washeated in a flow of acidic atmosphere having the same composition thatemployed above from 120 C. to 340 C. under the same condition thatemployed in the case mentioned above but under tension. The linearshrinkage of the fiber with the treatment of imposing stress during theheat treatment corresponded to 96% of that of the fiber without thetreatment of imposing stress. This fiber also was preoxidized with airin the same way. Both of the preoxidized fibers were heated in an acidicatmosphere containing 40% of hydrochloric acid and 60% of nitrogen bybeing moved successively through a zone from 250 C. to 550 C. in 35minutes, a zone from 550 C. to 1100 C. in 40 minutes and a zone at 1100C. in 10 minutes. The 1100 C. fiber without the treatment of imposingstress exhibited a tensile strength of 10.5 10 kg./cm. and modulus of9.5 10 kg./cm. and its yield was 42% by weight. The 1100 C. fiber withthe treatment of imposing stress exhibited a tensile strength of13.4)(10 kg./cm.

Example 19 The carbon fiber obtained in Example 18 was heated from 1200C. to 2600 C. at a rate of 550 C./hr., and was held at this lattertemperature for 35 minutes. During this heat treatment at 2600 C. thefiber was imposed stress and stretched by 8%. The unstretched 2600 C.fiber exhibited a modulus of 21.O 10 kg./cm. but the stretched 2600 C.fiber a modulus higher by 9% than this value.

Example 20 The fiber obtained in Example 14 was heated in a flow ofacidic atmosphere containing 10% of hydrochloric acid and 90% ofnitrogen from 200 C. to 480 C. at a rate of 12.0 C./hr., and then washeated in a flow of nitrogen gas to 1200 C. at a rate of 300 C./hr. Aportion of this fiber was heated in a flow of argon gas to 2800 C. at arate of 500 C./hr., and was held at this temperature for 54 minutes.During the heat treatment at 2800 C. the fiber was held under tensionand was stretched by 18%. Another portion of the 1200 C. fiber also washeated to 2800 C. under the same condition that above, but a stress wasnot imposed on this fiber. This 2800 C. fiber exhibited a modulus of 2310 kg./cm. but the stretched 2800 C. fiber a modulus higher by 24% thanthis modulus.

Example 20a A portion of the carbon fiber obtained in Example 17 washeated in a flow of nitrogen gas from 1500 C. to 2900 C. at a rate of560 C./hr. and at 2900 C. for 20 minutes. During the heat treatment at2900 C. the fiber was held under tension and was stretched by 26%.Another portion of the carbon fiber obtained in Example 17 was heated to2900 C. under the same condition that above, but a stress was notimposed on this fiber. This fiber exhibited a modulus of 24.1 kg./cm.but the stretched 2900 C. fiber a modulus higher by 28% than this value.

Example 21 A bundle-like mass of the dehydrated polyvinyl alcoholicfiber obtained in Example 14 was heated in a flow of acidic atmospherecontaining 6.0 of hydrochloric acid and 94% of nitrogen gas from 200 C.to 650 C. at a rate of 240 C./hr. and from 650 C. to 1300 C. at a rateof 350 C./hr. The fiber was held at 1300 C. for 30 minutes. The tensilestrength of this fiber was 10.8 10 kg./cm. and the yield of was 42%.

12. Example 22 A bundle-like mass of yarns of polyacrylonitrilefilamentary fiber (5 denier per filament and bright) was heated in aflow of hydrochloric acid vapor from 160 C. to 420 C. at a rate of 120C./hr. and was held at this latter temperature for 10 minutes. Theblackened fiber obtained was thermally stable, flexible and electricallysemiconductive. The yield was 88%.

Example 23 Bundle-like masses of filamentary fiber of acrylic polymermaterial containing 85% of acrylonitrile and 15% of methylmethacrylateby weight of monomer in polymer form (1.5 denier per filament andbright) was heated in a flow of acidic atmosphere containing 40% ofhydrochloric acid and of nitrogen gas by volume or in a stream ofatmosphere containing only nitrogen from 200 C. to 440 C. at a rate of180 C./hr. This 440 C. fibers were further heated in a flow of nitrogengas to 800 C. at a rate of 250 C./hr. The tensile strength and yield ofthe 800 C. fiber with the treatment in acidic atmosphere were 86x 10 lg./cm. and respectively. This yield corresponded to 152% of the yield ofthe 800 C. fiber without the heat treatment in acidic atmosphere.Another portion of the same starting fiber that used above also washeated under the same conditions that in the case of the fiber with thetreatment in acidic atmosphere men tioned above, but this fiber wasimposed stress, during the heat-treatment from 200 C. to 440 C. Thelinear shrinkage of the 440 C. fiber with the treatment of imposingstress was 38% of that of the 440 C. without the treatment of imposingstress. The 800 C. fiber with the treatment of imposing stress exhibiteda tensile strength of 12.4 10 kg./cm.

Example 24 A bundle-like mass of continuous filament of acrylic materialcontaining 90% of acrylonitrile and 10% of vinyl chloride was heated ina fiow of acidic atmosphere containing 20% of hydrochloric acid and ofnitrogen from 200 C. to 500 C. at a rate of 40 C./hr. and from 500 C. to750 C. at a rate of 200 C./hr. The yield of the 750 C. fiber was 68%,which corresponded to 148% of the yield of the 750 C. fibrous massobtained by heating another portion of the same starting fiber that usedabove solely in nitrogen under the same condition of raisingtemperature. This fiber exhibited a tensile strength desired forindustrial needs.

Example 25 A plain weave fabric woven relatively loosely of warps andfiles of staple fiber threads of acrylic fibrous material containing 80%of acrylonitrile (3 denier per single staple fiber) was treated with anaqueous dispersion of silica fine particle powder to substantially fillthe voids among staple fibers. After it had been dried in an oven, thefabric was heated in a flow of hydrochloric acid vapor from 250 C. to350 C. at a rate of 60 C./hr. and from 350 C. to 480 C. at a rate of 10C./hr. From this 480 C. fabric, silica powder solids were removed byWashing successively the fabric with an aqueous solu tion ofhydrofluoric acid and with water. The fabric obtained exhibited a highflexibility and termal stability. The yield was 83%, which correspondedto 157% of the yield of fabrics (brittle) obtained by heating anotherportion of the same starting fabric that above solely in nitrogen.

Example 26 The flexible fabric obtained in Example 25 was heated in aflow of acidic atmosphere containing 10% of hydrochloric acid andnitrogen from 480 C. to 800 C. at a rate of 160 C./hr. and from 800 C.to 1200 C. at a rate of 200 C./hr. The carbon fabric having a highflexibility was obtained.

Example 27 A bundle-like mass of filamentary fiber of polyacrylonitrile(2 denier per filament) was preoxidized by being heated in air at 200 C.for hours and from 200 C. to 300 C. at a rate of 100 C./hr. Theblackened fiber was obtained. This fiber was further heated in a flow ofhydrocloric acid from 200 C. to 500 C. at a rate of 460 C./hr. The yieldof this 500 C. fiber was 85% by weight, which corresponded to 138% ofthe yield of the 500 C. fiber obtained by heating another portion of thesame starting fiber that used above under the same condition of raisingtemperature that employed above in air and then in nitrogen.

Example 28 A bundle-like mass of filamentary fiber prepared from acrylicpolymer material containing 95% of acrylonitrile, having a substantiallyparallel fiber orientation was heated in air at 200 C. for 5 hours, andfrom 200 C. to 300 C. at a rate of 100 C./hr. After that, the fiber washeated a stream of acidic atmosphere of 40% of hydrochloric acid and 60%of nitrogen from 300 C. to 900 C. at a rate of 320 C./hr., and then innitrogen from 900 C. to 1200 C. at a rate of 420 C./hr. The yield was63%. The tensile strength was 11.0 kg./cm. These yield and tensilestrength corresponded to 121% and 128% of the yield and tensile strengthof the 120 C. fiber obtained by heating another portion of the samepreoxidized fiber that used above only in nitrogen from 300 C. to 1200C. under the same conditions of raising temperature that employed above,respectively.

Example 29 A polyacrylonitrile filamentary fiber mass was heated in aflow of acidic atmosphere containing 40% of chlorine gas and 60% ofnitrogen at 200 C. for 30 minutes and then at 240 C. for 10 minutes. Ablackened fiber was obtained. This fiber was heated in a flow of acidicgas containing 10% of hydrochloric acid and 90% of nitrogen from 250 C.to 460 C. at a rate of 5 C./hr., from 460 C. to 800 C. at a rate of 60C./hr., and from 800 C. to 1300 C. at a rate of 180 C./hr. The tensilestrength and the yield of the 1300 C. fiber were 9.1 x 10 kg./cm. and58%, respectively. These values corresponded to 128% and 124% of thetensile strength and the yield of the 1300 C. fiber obtained by heatingonly in nitrogen another portion of the same 240 C. fiber preoxidizedwith chlorine that obtained above, respectively.

Example 30 A continuous yarn of acrylonitrile filamentary fiber waspreoxidized by being moved in air through a heating zone from 190 C. to260 C. in 30 minutes with imposed stress or without imposed stress.After that, the preoxidized yarns were heated by being moved through azone from 260 C. to 450 C. in a flow of hydrochloric acid vapor in 45minutes, and then through a zone from 450 C. to 940 C. in a stream ofnitrogen in 40 minutes. The linear shrinkage of the fiber with thetreatment of imposing stress during the heat treatment to 450 C. was 26%of that of the 450 C. fiber without the treatment of imposing stress.The 940 C. fiber with the treatment of imposing stress exhibited atensile strength of l2.8 10 kg./cm. and the 940 C. fiber without thetreatment of imposing stress a tensile strength of 11.6 10 kg./cm Theyield was 67%, which corresponded to 124% of that of the 940 C. fiberobtained by heating only in nitrogen from 260 C. to 940 C.

Example 31 A portion of the continuous yarns of 940 C. carbon fiberprepared by heating another portion of the same starting fiber that usedin Example 30 under the same condition that employed in Example 30 were.heated by being moved in an argon flow through a zone from 1000 C. to2500 C., and in 45 minutes through a zone at 2500 C. During the heattreatment at 2500 C., the fiber was imposed stress and was stretched by28%. Another portion of the 940 C. carbon fiber yarn was heated to 2500C. under the same condition than employed above, but without imposedstress at 2500 C. The stretched fiber exhibited a modulus 20.8 10kg./crn. which corresponded to 108% of that of the unstretched fiber.

Example 32 Continuous yarns of acrylic filaments were heated by beingmoved in air through a zone from 180 C. to 300 C. in 40 minutes withimposed stress or without imposed stress. The preoxidized fiber yarnswere heated in a flow of acidic atmosphere containing of hydrochloricacid and 20% of nitrogen through a heating zone from 300 C. to 560 C. inminutes, through a heating zone from 560 C. to 1100 C. in 60 minutes andthrough a zone at 1100 C. in 16 minutes. The linear shrinkage of the 300C. fiber with the treatment of imposing stress was 25% of that of the300 C. fiber without the treatment of imposed stress. The yield and thetensile strength of the 1100 C. fiber with the treatment of imposingstress were 62% and 14.6)(10 kg./cm. respectively. The tensile strengthof the 1100 C. fiber without the treatment of imposing stress was '11.310 kg./cm.

Example 33 A portion of the carbon yarn with the treatment of imposingstress obtained in Example 31 was heated by being moved, in a nitrogenflow, through a zone from 1100 C. to 27 C., and in 55 minutes through a2700 C. zone. During the heat treatment at 2700 C. the fiber was imposedstress and stretched by 18%. The stretched fiber exhibited a modulushigher by 24% than that, 21.9)(10 kg./cm. of the unstretched fiber.

Example 34 A continuous yarn of filamentary fiber of acrylic materialcontaining of acrylonitrile by weight of monomer in polymer form washeated by being moved through a zone from 190 C. to 450 C. in 40 minuteswith imposed stress in an acidic atmosphere containing 50% ofhydrochloric acid and 50% of nitrogen by volume. The 450 C. yarn wasfurther heated by being moved successively through a zone from 450 C. to800 C. in 30 minutes and through a zone from 800 C. to 1200 C. in 25minutes. The linear shrinkage of the 450 C. fiber with the treatment ofimposing stress during the heat treatment to 450 C. was 48% of theshrinkage of the 450 C. fiber without the treatment of imposing stress.The 800 C. fiber with the treatment of imposing stress exhibited atensile strenght of 128x10 kg./cm. and a modulus of 13.8 X10 kg./crn.

1 Example 35 The carbon yarn obtained in Example 33 was heated in anargon stream, in a tunnel furnace, by raising the temperature from 1500C. to 3000 C. at a rate of 400 C./hr. and then by holding at 3000 C. for30 minutes. During the heat treatment at 3000 C., the fiber yarn washeld under tension and was stretched by 26% by length. This carbon fiberexhibited a modulus higher by 34% than that, 23 10 kg./cm. of theunstretched fiber.

I claim:

1. A process for the preparation of a carbonaceous fiber which comprisestreating a fiber selected from the group consisting of polyvinylalcoholic and acrylic fibers in an atmosphere containing from 10 tohydrogen chloride, the remainder being inert gas, said atmosphereflowing over said fiber at a rate sufiicient to remove gases resultingfrom decomposition of said fiber, at a temperature between and 1500 C.

2. A process according to claim 1 where in the fiber is stretched attemperatures below 450 C. during the treatment with hydrogen chloride.

3. A process wherein the product of calim 1 is heated in an inertatmosphere at temperatures up to 300 C.

4. A process according to claim 3 wherein the fiber is stretched attemperatures between 2500 C. and 3000 C.

5. A process according to claim 4 wherein the stretching is between 5and 40%.

6. A process according to claim 1 wherein the fiber is polyvinylalcoholic.

7. A process according to claim 6 wherein the polyvinyl alcoholic fiberis partially oxidized :before the hydrogen chloride treatment.

8. A process according to claim 1 wherein the fiber is acrylic.

9. A process according to claim 1 wherein the acrylic fiber is partiallyoxidized before the hydrogen chloride treatment.

10. A process according to claim 8 wherein the acrylic fiber ispolyacrylonitrile.

11. A process according to calim 6 wherein the poly- 16 vinyl alcoholicfiber is treated with the hydorgen chloride atmosphere at temperaturesbetween and 450 C. 12. A process according to claim 8 wherein theacrylic fiber is treated with the hydrogen chloride atmosphere attemperatures between 250 C. and 450 C.

References Cited EDWARD J. MEROS, Primary Examiner U.S. C1. X.R.

UNrrm s'rA'ms PATENT OFFICE CERTIFIECATE OE? CORRECTION PatentNo.3,529,934 Dated September 22, 1970 Inventor( AKIO SHINDO It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 15:

Claim 3, change "calim" to claim line 2 change "300C" to 3000C 6m) AmIII- I. m a. EdwardlLFletchcnIr.

Auesting Officer

